Laminators have been used in the art to apply photoresist layers onto circuit panels. Foil webs made up of a protective polyethylene layer, a photoresist layer, and a Mylar protective foil have been supplied from rollers and are continuously laminated to both sides of the circuit panels. Subsequently, the thus obtained webs are cut at the respective edges of the workpieces.
U.S. Pat. No. 3,658,629 discloses an improved photoresist applicator in which a pair of vacuum-connected drums are utilized to supply the foil webs to both sides of a circuit panel. Pressure strips on the circumference of the drums serve to affix the foil webs to the drums. After the removal of the protective layer thereon, the foil webs are removed from the drum circumference owing to the continuous drum rotation. Subsequently, the workpieces pass through heated laminating rollers in order to secure the foil onto the workpiece. A disadvantage of this design is that the foil can prematurely detach itself from the drum circumference. As a consequence, the foil could prematurely come into contact with the surface of the workpiece, causing wrinkles to form when the foil is laminated onto the workpiece. Furthermore, in this device only uniform foil segments can be cut, and consequently only workpieces of a predetermined size can be processed.
Another laminator is described in U.S. Pat. No. 4,025,380. The foil webs are applied to the leading edge of the heated workpiece by means of vacuum bails moving back and forth in a sliding mechanism. The webs are affixed with their leading edges before laminator rollers are activated. Position sensor switches activate the bails as well as the cutter mechanism. The switches can be adjusted so that different lengths of workpiece and foil segments can be handled The trailing edges of the foil segments are drawn over vacuum shoes after cutting, which prevents the foil from prematurely contacting the workpiece surface.
The foregoing and other laminating devices suffer from a common operational deficiency. During lamination the workpieces do not move in a continuous fashion; rather they have to be stopped when the foil (most of which is already laminated) is cut to the required length. This stoppage of the workpiece (or panel) during lamination frequently causes an undesired prepolymerization. Specifically, the laminator rollers are heated to ensure a safe application of the lamina onto the surface of the workpiece, even if the workpiece itself has been heated previously. The photoresist-coated workpiece undergoes concentrated heating upon standstill, causing prepolymerization. This disadvantage increases in magnitude with the increase in intricacy of the conductive lines of the panel. Therefore, in view of the progress in miniaturization of circuit patterns in the art, elimination of the above-described deficiency is required.